The growing demands on mobile networks to support data applications at higher throughputs and spectral efficiencies have driven the need to develop Orthogonal Frequency Division Multiplexing (OFDM) based 4th generation (4G) networks including third generation partnership project, 3GPP, Long Term Evolution (LTE) networks. Because of the scarcity of spectrum, the same frequencies are reused at all cell sites. The resulting interference limited system will not achieve the full potential capacity that the LTE standard can support without the implementation of one or more interference mitigation and/or cancellation techniques. Interference mitigation and/or cancellation techniques have been investigated and deployed with varying degrees of success in mobile networks for over 20 years. Traditional approaches have focused on ensuring orthogonality between transmitted signals in time or frequency. Other systems operate spatially or by actively removing and cancelling interfering signals from the desired signal.
In early second generation, 2G, cellular systems, orthogonality was achieved primarily through static pre-planned allocations of radio resources. Third generation, 3G, systems introduced interference cancellation techniques based mostly on a combination of blind information gathered at a base station such as spectrum usage monitoring and coarse exchange of interference indicators such as the Rise over Thermal (RoT) indicator employed in the 3GPP 1xEV-DO standard. Typically interfering signals have been estimated using blind detection and their estimates subtracted from the desired signals.
In 4G networks, the advanced evolution of LTE has focused on Coordinated Multipoint (CoMP) as a means to improve performance of the air interface. The central concept of Uplink Coordinated Multipoint (UL CoMP) is that although a user equipment, UE, is served by one cell, the neighboring cells may receive the UE's signal with sufficient quality such that they may be able to contribute to the reception and processing of the UE's signal and payload.
Referring now to the drawing figures, in which like reference designators denote like elements, there is shown in FIG. 1 a diagram of one embodiment of a known coordinated multi-point network 10. The network 10 includes a plurality of geographically dispersed user equipment mobile terminals 14a, 14b, 14c, referred to collectively herein as user equipment (UE) 14, each located within a corresponding geographic area 16a, 16b, 16c referred to collectively herein as cells 16. Each cell 16 is served by a respective base station 12a, 12b, 12c, referred to collectively herein as base stations 12. Each base station 12 receives uplink signals from the UEs 14 and processes (e.g., decodes) the uplink signals to recover information symbols therein.
A base station, e.g., base station 12a, serving certain UEs, e.g. UE 14a, may nonetheless also receive uplink signals from other UEs, e.g., UE 14c, located within another cell, e.g., cell 16c. Rather than simply treating such uplink signals as inter-cell interference, the base station 12a cooperates with the serving base station 12c of UE 14c. In particular, the base station 12a sends the uplink signals to the serving base station 12c of UE 14c over a backhaul communication link 18 between the base stations 12. The serving base station 12c of UE 14c then jointly processes the uplink signals it received itself and the uplink signals received from other base stations 12 in order to mitigate inter-cell interference. It will be understood that in some embodiments, multiple cells may be serviced by a single base station. Thus, for example, two or more cells may be hosted from a common physical location. In these cases, a CoMP payload may be shared between cells hosted at the same physical location by connections between entities at the physical location. These connections may be inter-card or inter-unit connections.
Any given base station, e.g., base station 12a, therefore operates as a serving base station with respect to UEs 14 located within its served cell, e.g. cell 16a, while operating as a so-called cooperating base station with respect to UEs, e.g., UEs 14b and 14c located within another cell, e.g., cell 16b and/or cell 16c. Likewise from the perspective of any given mobile terminal, e.g., UE 14a, one base station 12a operates as the serving base station for the UE and other base stations 12b and 12c operate as cooperating base stations for that UE. Thus, a given base station such as the base station 12a performs serving base station functions 13a and cooperating base station functions 13b. 
In systems where the CoMP payload is not a streaming type, but is rather a payload that is computed at the cooperating base station, the cooperating base station must compute and transmit the CoMP payload in time for the serving base station to use the CoMP payload to decode the UE transmission. The hybrid automated request, HARQ, timing within an exemplary LTE system is 4 milliseconds so that the CoMP payload should be delivered within, for example, 500 micro-seconds of receiving the transmission from the UE.
FIG. 2 is a timing diagram for implementing CoMP assistance according to known methods. In row 1, time slot 0, a grant requesting a transmission from a UE is transmitted by the serving base station. Row 4, time slot 0, shows a CoMP assistance request being transmitted by the serving base station. The label {D,S} indicates that the transmission of the CoMP assistance request is delay tolerant and of short payload size. Row 5, time slot 0, shows the CoMP assistance request being received by the cooperating base station. In row 2, time slot 4, the UE transmission is received by the serving base station and the cooperating base station. In row 6, time slot 5, the UE transmission is processed by the cooperating base station.
In row 7, time slot 6, a CoMP payload is determined by the cooperating base station based on the processed UE transmission. This CoMP payload is transmitted to the serving base station in time slot 6. The label {U,L} indicates that the CoMP payload is delay intolerant and of large payload size. Meanwhile, in row 3, time slots 5-7, the serving base station decodes the received UE transmission with the help of the CoMP payload. In row 1, time slot 8, a grant requesting transmission of a next block by the UE is sent to the UE from the serving base station. This next block is received by the serving base station and the cooperating base station in time slot 12. Decoding of this second UE transmission by the serving base station occurs after time slot 12, in row 3.
Since the timing of the base stations are synchronized, the short latency required for CoMP payload delivery—the CoMP payload being transmitted by time slot 6—results in undesired high peak data rates between the cooperating base stations and the serving base stations. After provisions are made to allow multiple cells to share with neighboring cells, the amount of required inter cellular bandwidth may easily exceed the non-CoMP case by a factor of 20 to 40 times. Further, this places a heavy load on processing power at the cooperating base stations to compute the CoMP payloads.